2.1. NEUROLOGICAL MOVEMENT DISORDERS
Components of the human nervous system which control movement may be classified into the following five categories: (1) "upper" motor neurons located in the cerebral cortex and their fiber projections to "lower" motor neurons in the spinal cord; (2) lower motor neurons in the spinal cord and their fiber projections to neuromuscular junctions; (3) brainstem nuclei which project to the spinal cord and control posture, automatic and repetitive movements; (4) two subcortical systems, namely the basal ganglia and the cerebellum, which control muscle tone, posture, and coordination of movement; and (5) cortical structures, such as the premotor and accessory motor cortex, which are involved in the planning and programming of voluntary movement (Adams and Victor, 1985, Principles of Neurology, Third Edition, McGraw-Hill Book Company, New York, pp.35-36). Conditions which disturb the structure and/or function of these components give rise to movement disorders that may be associated with paralysis, lack of coordination, or adventitious movements such as tics and tremor (Id.)